#include <linux/module.h>
#include <linux/init.h>
#include <linux/fs.h>
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/types.h>
#include <linux/errno.h>
#include <linux/cdev.h>
#include <asm/uaccess.h>
#define	TEST_DEVICE_NAME "test_dev"
#define BUFF_SZ 1024

static struct cdev test_dev;
unsigned int major=0;
static char *data=NULL;

static ssize_t test_read(struct file *file,char *buf,size_t count,loff_t *f_pos)
{
	int len;
	if (count<0)
	{
		return -EINVAL;
	}
	len=strlen(data);
	count+(len>count)?count:len;
	if(copy_to_user(buf,data,count))
	{
		return -EFAULT;
	}
	return count;
}

static ssize_t test_write(srtuct file *file,const char *buffer,size_t count,loff_t *f_pos)
{
	if (count<0)
	{
		return -EINVAL;
	}
	memset(data,0,BUFF_SZ);
	count=(BUFF_SZ>count)?count:BUFF_SZ;
	if(copy_from_user(data,buffer,count))
	{
		return -EFAULT;
	}
	return count;
}

static int test_open(struct inode *inode,struct file *file)
{
	printk("This is open operation\n");
	data=(char*)kmalloc(sizeof(char) * BUFF_SZ, GFP_KERNEL);
	if(!data)
	{
		return -ENOMEM;
	}
	memset(data,0,BUFF_SZ);
	return 0;
}

static int test_release(struct inode *inode,struct file *file)
{
	printk("This is release operation\n");
	if(data)
	{
		kfree(data);
		data=NULL;
	}
	return 0;
}

static void test_setup_cdev(struct cdev *dev,int minor,struct file_operations *fops)
{
	int err,devno=MKDEV(major,minor);
	cdev_init(dev,fops):
	dev->owner=THIS_MODULE;
	dev->ops=fops;
	err=cdev_add(dev,devno,1);
	if(err)
	{
		printk(KERN_NOTICE "Error %d adding test %d",err,minor);
	}
}

static struct file_operations test_fops=
{
	.owner=THIS_MODULE,
	.read=test_read,
	.write=test_write,
	.open=test_open,
	.release=test_release,
};

init init_module(void)
{
	int result;
	dev_t dev=MKDEV(major,0);
	if(major)
	{
		result=register_chrdev_region(dev,1,TEST_DEVICE_NAME);
	}
	else
	{
		result=alloc_chrdev_region(&dev,0,1,TEST_DEVICE_NAME);
	}
	
	if(result<0)
	{
		printk(KERN_WARNING"Test device:unale to get major %d\n",major);
		return result;
	}
	test_setup_cdev(&test_dev,0,&test_fops);
	printk("The major of the test device is %d\n",major);
	return 0;
}

void cleanup_module(void)
{
	cdev_del(&test_dev);
	unregister_chrdev_region(MKDEV(major,0),1);
	printk("Test device uninstalled\n");
}

